Quantitative histopathologic assessment of developing phenytoin-induced gingival overgrowth in the cat.

Phenytoin (Dilantin) induces gingival overgrowth characterized by an accumulation of connective tissue The cell-to-matrix ratio in the mature lesion is normal, yet there must be more fibroblasts per oral cavity if there is excessive tissue mass. Using a mongrel cat model system, we studied the early, developing phenytoin-induced lesion by quantitating fibroblasts per unit of tissue in papilla biopsies collected over a 3-month period of daily drug administration. At 6 and 8 weeks, the number of fibroblasts per unit of tissue increased dramatically. By 3 months, as the lesions matured, the fibroblast-to-matrix ratio returned to normal. We suggest that the drug interacts with resident gingival fibroblasts, causes them to proliferate and thus induces a true, but transient, hypercellularity. Cell division then appears to slow or cease, and rapid production of connective tissue matrix ensues, returning the cell-to-matrix ratio to normal.